When do you give up, and other questions

I have several questions, which I'm posting behind the lj-cut in order to save your friendslists the multiple posts.
1) Has anyone had any experience with Spring Hill Nursery? I ordered a large number of plants from them, but only about a fourth of the total order have shown any signs of life, and a few of those thrived for a short time and then died. What plants lived are doing well, but I'm not sure whether the majority of the plants dying or never really living is a reflection on them or on my gardening skills. (I did follow their directions in planting, keep the plants watered, etc.)
2) Of the plants that thrived for a short time and then went kaput, one was a Japanese maple and the other a dwarf burning bush.
A) the Japanese maple--after growing well for a couple of months, the leaves suddenly turned brown/gold and papery and have now more or less shriveled up. I've kept watering it, just in case there's any point, but I'm wondering if I should just pull it out/cut it down to ground level (the trunk is only a little thicker than a pencil at this point), or if there might be some hope for it.
B) the dwarf burning bush--the leaves got fungus-y spots on them and fell off. The stems are still green-ish looking, but they haven't had leaves for several weeks. Again, do I pull it out/cut it to the ground, or is there hope?
3) I'm trying to plan ahead for fall. Since this is my first time to ground-garden, I have no real idea what needs to be done. I'd like to pull the perennials out of the garden, get some compost (or something else beneficial) and till it into the ground, and then replant the perennials. Am I barking up the right tree here at all?
4) My "lawn" is a (not so) lovely collection of dallis grass, cockleburs, and at least one or two other kinds of grass all mixed together. Is there any way to eliminate the undesirable growth (the dallis and the cockleburs, mainly) without killing the whole lawn? (I try to avoid solutions that are dangerous to me, my pets, or ground water.)
5) I have aphids, sugar ants, and who knows what else living in the garden. I'd like to attract (and keep, if possible), some beneficial critters to feed on the not so beneficial ones. I know I can buy ladybugs, etc., but how do you convince the critters to hang around after you let them loose? (I realize that this question probably shows my ignorance, but I really know nothing about this subject, so any education you can give me would be great!)
6) Part of my Spring Hill order included one climbing rose bush and two fairy rose bushes. I haven't ever seen anything that indicates growth (including any signs of green) in spite of following the directions in planting and watering. Is there any point in leaving them in the ground?